Manufacture of rolled-steel members



Patented May 7, 1.929.

UNITED STATES PATENT OFFICE.

NARAINA (lHOPR-A AND FREDERICK JOHN BULLEN, OF WESTMINSTER, LONDON,

. ENGLAND.

MANUFACTURE OF ROLLED-STEELE; SMEMBERS.

No Drawing. Application filed December 10, 1926, Serial No. 154,028, and in Great Britain January 2, 1926.

This invention relates to the manufacture of rolled steel members and for the sake of convenience will be described by reference to the manutactinc of steel rails as typit'ying rolled steel members. It is to be understood, however, that the invention is not limited to the manufacture of steel rails but is applicable to the manufacture oil any form of rolled steel member.

In the ordinary manufacture of steel rails there occurs a zonic heterogeneity of structure which may be said to be characterized by the presence oi three zones, namely, a central zone of pearlitic nature, an outer zone of soft decarburized steel, and an intermediate Zone of high-carbon steel. This zoning of structure is generally accompanied by a state or internal instability, and has been found to be mainly responsible for the faults commonly experienced in rails, of corrugation and eX- cessivo wear and tear in use.

It is known to be possible to remove from steel detects ol" the kind referred to above by annealing, i. e. by a treatment comprising heating the steel to a high ten'iperature and thereafter allowing the metal to cool slowly. Such ti-eatn'ient, however, is gei'ierally associated with the disadvantage of producing softening of the steel; it does not eliminate from the structure of the steel the aforesaid zonic heterogeneity, and, further, it leads to the formation of scale, with an accompanying loss of steel by weight.

According to the present invention, a proc es of manufacture ofrolled steel members is characterized inthis, that the hotmember from which the rail is being formed is submitted one or more times during the formation of the rail, for example, between successive rolling operations, to a treatment which involves a temperature drop to a point below the lowest change-point oi the metal and following this a reheating of the member to the appropriate temperature for the succeeding forming operation. By lowest change point, we mean the lowest critical point, and have designated this point in some of the claims as the Ar change point, in accordance with common practice.

The effect of heat-treatment according to the invention is to remove the aforesaid structural defects, or, according to circumstances,

materially to reduce them; and where such detects are not wholly removed the hot memher may besubjected after completion of its forming operations, to the final heat-treatment process set forth in the specification of our British Letters Patent, No. 271,529 of 1927 That is to say, the hot completelytormed member may be cooled to a temperature below the lowest change-point ofthe metal, then heated to a temperature above (e. g. above) the highest change-point, cooled gradually to a temperature somewhat below (e. g. 50 C. below) the lowest changepoint, and finally allowed more rapidly to cool, e. g. by allowing the member to cool spontaneously in the atmosphere.

lVe have found it preferable, and it is a further feature of this invention, to conduct the heat treatment characterizing this invention in the presence of an oxidation inhibitor by which is meant a solid material which is non-fusible at the temperature employed in the heat treatmentand the action otwhich, through chemical aflinity of the material towards the deleterious :turnace gases, is to protect the metal from oxidation or substantially to reduce the degree thereof. Examples of oxidation inhibitors are alkaline earth oxides, such as lime; ini'usible readily-oxidizable materials in a condition to present to the gases a large. surface relatively to the area of the exposed sur'tace of the member under heat treat ment, for example, shavings or turniugs of an oxidizable metal such as steel; and carbonaceous material, such as an exhausted carburizing mixture, boiler-ash or producer-ash, containing an adequate proportion (for example, at least 10 per cent) of combustible carbon.

By an exhausted carburizing mixture is meant a carburizing mixture which has been used to such an extent as to render it unsuitable i or further use in carburizin A suitable carburizing mixture which, when exhaust-ed, has been found to be utilizable according to the present invention consists of three parts of powdered beech charcoal and two parts each of powdered horn charcoal and powdered animal charcoal. The boiler-ash or producer-ash may be of the type. which usually contains from 5 to 15 per cent of carbon.

The use in heat-treatment of steel of a mixture of alkaline earth oxide and an appropriate carbonaceous material carrying free carbon such as an exhausted carburizing reagent, forms the subject of our British Letters Patent No. 271,606 of 1927, and is claimed herein only in conjunction with the special. heat- Ill treatment whichcharacterizes the present in vention.

'The beneficial effects of the process according to the present invention are generally found to 'be influenced by the degree of cooling to which the member is subjected between the forming operations; and in such cases,'-where commercial exigencies permit, thev cooling may, with advantage, be carried to a degree considerably below the lowest 'ch'ange-pointof the metal, and'even to atmosjp'h'eric temperature.

We have frequently found in our work "upon steel members that the process of this invention gives specially good results in the case'of steel containinga small proportion of a metallic'elem'ent,such as nickel or cobalt, the presence of which tends to depress the change-points of the steel.

' According to a further'ieature of the invention, therefore, the steel member subjected to the a foresaid special heat-treatment is composed ofsteel containing asmall proportion of a metallic change-point depressant, such, forexampl'e, as nickel or cobalt.

The proportion necessary of such element is preferablyquite small, forexample, 1 per cent -or less. Wi e have usually t'oundbii? per cent to be. su'flicient. In this connection it will be understood that the 'advantage in question is secured "with steel wherein the nickel "or other change-point depressant is present evenas an adventitiouscomponent.

e have also found that the heat-treatment characteristic oft-his invention is specially'eifeCtive in the caseof chrome steels; and-according to a turther feature of the invention the steel member subjected to heattreatment as above composed of chromesteel. 'We have found that with this partic- 'ular special metal theadvantageous effects of "the invention are frequently very marked.

"The chrome steel from which the member deformed may with further advantage be a chrome-steel containing a change-point depressa nt,suchas nickel orcobalt.

Reverting again to the oxidation inhibitors the presence of which as aforesaid is preferable-during the heat-treatment which characterizes this invention, the inhibitor may comprise sheets or plates-of an-oxidiza- 'b'le metal sueh as iron or steel d'isposed around the walls of the furnace-or beneath the root thereof -or in the gas openings. Alternati' vuelygthe steel memberto be protected may be enveloped during the heat-treatment in aca'gebuilt up of sheets or plates or bars of iron or steel or other readily oxidizable metal.

Agaimifan alkaline earthoxide such as lime be'employed as the oxidation inhibitor it'may be'emp'loyed in powder form or in aqueous suspension or solution. The man'- 'ner ofapplying the oxide maybe varied ac- :eord/in'g to circumstances and convenience. It the :member Pun'der heat-treatment is the either-asan alternative'to the aforesaid forms and modes of application of oxidation in liibitor -or in conjunction therewith to line ithesoaking pit-orother furnace with dolomite-or furnaceslag.

Lastly, with regard to the oxidation inhibitors, any 'two or more of thaforesaid forms may be employed conjointly.

E awn/p10 1.

Two ingots were cast. with the following analyses':

A. ll. llrr rm! Prr rem Carbon 564i 563 Silicon .112 l .112 Sulphur .033 i .0324 Phosphorus .043 y .043 Manganese .80 i .80 N iekel ,l 1)..

The tapping teun crntures were 1530 (l. 1520 C.

The teaming temperatures (with one inch :nozzle) were 145(l -C. 1450 (l.

'Ingot A. was treated and rolled right through, according to the normal practice :prewliling in the steel works.

IngotB. was treated and rolled in accord- :ance with the present invention. The top ol' the ingot mould wascovered (luring setting with'an'oxidation protector as aforesaid consisting of an exhausted carburizing mixture. On stripping, the ingot was spread over with the-a'lol'esai d oxidationprotector. The sh-i rping temperature was 960 C. The ingot was transferred to the soaking pit, the floor of which was covered'to adepth of about-three inches with a mixture-0t boiler'nshrca rrying 15.6 per cent. of combustible carbon, and lime, in the proportions-0t 10. while sufficient steel turnings to cover, when loosely spread, asuni ace of at least half an inch along the bed of the pit, were packed therein around the ingot. The top lids of the pits were provided with a mass of-steel turnings so suspended from the lids that practically the whole space between the top-of 'the in got and the roof of the furnace was occupied by the turnings. The ingot was transferred to the eogging mill at 1190 C. The billet passed the saw at a temperature of 940" C. and wasthen allowed to cooldown 'to'600 The cooling down'was oarriedout with the billet covered with an oxidation protector Til Hill

lllfi lltl lli'i till Max- Elonga- Reducimuiu tlon on tion of strength. 3". area.

Per cent. Per cent. Sample A 53. 24 ll 16. 3 Sample 13 53. 42 18 27. 4

The structure of the rail showed itsel'l to be in a homogeneous pcarlit-ic i oi'n'i, and the rail exhibited no sign of a dccarburized zone at the surface.

Example (3.

The analysis olthe steel. was as follows l'cr cont. Carbon u .563 Silicon .196 Sulphur .0333 Phosphorus s... s l......s -.h. .036 lllanglunesmnl .73 Nickel .35 Chromium l- .98

The operations of pouring, teaming, cogging, and rolling Were carried through as in the case oi sample ll of Example l.

The billet reached the saw at 920 G, was then cooled down to (350 C. and reheated to ill-(7 (1, both. cooling and reheating being; conducted in the presence ol? an oxidation protector as in Example 1.

' 'lhe billet was then subjected to rolling operations to fOIJIl a rail. The test figures fore as follows l Maximum Reduction Strength. Elongation. of urea 131 well. 5]. 36 20. i1. 3. 7/269 I ln this case the increase of elongation and reduction of area of test piece Without loss ot' tensile strength was even more marked than in the case of the sample B product of lihunnple l.

The corrcspondinp,- figures for a rail produced by ordinary steel works practice and of the same analysis Were:

Maximum 1 Reduction Strength. ltlOl'lgAtlOIl. of area Biinoll.

I it is to be understood, in conclusion, that the special heat-treatment which broadly characterizes this invention, namely, the treatn'ient which comprises cooling the hot partially-formed member to a temperature below the lowest change-point oi the metal, and following; this a reheating of the member to the appropriate temperature for the succeeding lt'ormiug, operation, may be applied to the member at any time during its formation, from the billet-stage onwards.

Vi e claim:

1. In the manufacture of rolled steel membcrs, interposiug, during the process of for mation of the member, a heat-treatment Whichcomprises cooling" the hot member through the Ar change-points ol the steel and thereafter re-heating to the temperature requisite to further formation, the re-heating operation being effected by direct contact with hot furnace gases which have been reudered substantially innocuous towards the the steel as regards their oxidizing and decarburizing capacity by treatment with both an alkaline earth oxide and a substantially .noircarbi'lrizing earhon-carrying material as herein defined.

2. In the manufacture of-rolled steel men1- hers, interposing, during the process of formation oi the member, a heat treatment Which comprises cooling the hot member through the Ar change-points of the steel in the presence of material. capable of inhibiting oxidation and thereafter reheating to the temperature requisite to further formation by direct con. tact with furnace gases which have been rendered substantially innocuous towards the steel as regards their oxidizing and decurburizing opacity by treatment With both an al lcaline earth oxide and a substantially noncarlmrizing 'arboircarrying material as herein delincd.

A process otl n'lauuiiacture of rolled steel members. according to claim 1, wherein the relative amounts of the reagents are such that the quantity of oxide is equivalent to from to by weight of the combined quanti. 10s of oxide and carbon-carrying material and the carbon content oi. the carbon-carryi ng material is such that the quantity of free carbon present is equivalent to from 4: /0 to 20% by Weight of the quantities.

4:. A process of manufacture of rolled steel members according; to claim 1, wherein the re heating operation is effected. in the presence of a false increase of area of oxidizable material provided. by a mass of infusible readily oxidizable material substantially as and for the purpose set forth.

5. In the manufacture of rolled steel members, interposing, during the process of formation of the member, a heat-treatment which comprises cooling the hot member through the Ar change-points of the steel and tlmreafter reheating to the temperature requisite to further formation, the reheating aforesaid combined operation beingefi'ected by direct contact with hot furnace gases which have been rensdered substantially innocuous towards the steel as regards their oxidizing and deearburlzing capacity by treatment with both ilime a'nd. a substantially non-carburizing carbon-carrying material as herein defined, the relative amounts of lime and carbon-carryinganaterial being such that the quantity of lime employed is equivalent to from to 50% by Weight of the combined quantities of lime and carbon-carrying material and the carbon content of the carbon-carrying anaterial is such that the quantity of free carbon. present is equivalent to from 4% to by Weight of the aforesaid combined quantities.

' :6. Aprocessof manufacture-of rolled steel 'members according to claim 5, wherein the reheating step is effected in the presence of a false 11101162186 ofiarea of oxidizable material 1 plovnled by a massof infusibre readily Okldlzablesmaterial.

7. A process of manufacture of rolled steel members according to claim 5, wherein the cooling step is effected in the presence of both lnneiand a substantlally non-carburizing carhon-carrying material as herein defined, the relative amounts of hme and carbon-carrying:

material being such that the quantity of lime employed is equivalent to from 10% to by Weight-of the combined quantities of lime .aIid carbon-carryin material and the carbon content of the car bou-carrying material is such that the quantity of free carbon present the presence of material capable of inhibiting oxidationof the steel, and thereafter reheatburizing carbon-carrying material as herein deiin ed; the relative amounts of the lime and carbon-carrying material being such that'the quantity of lime employed is equivalent to from 10% to by weight of the comhined quantities of lime and carbon-carrying material and. the carbon content of the carboncarrying material is such that the quantity of free carbon present is equivalent to from 4% to 20% by weight of the aforesaid combined quantities.

9 A processof manufacture of rolled steel members according to claim 8, wherein the furnace contains also a mass of infusihle readily oxidizable material providing a false increase of oxidiza'ble surface area .in exposure in the furnace to the furnace gases.

10. A process of manufacture o f rolled steel members according to claim 8, wherein the carbon-(arr'ying material is a carhurizing mixture which has been used to such an extent to have become substantially exhausted of its carburizing capacity.

11. A process of'manufactureofrolled steel members according to claim 8, wherein the steel of which 'the member is composed contains a small proportion of a change-point depressant.

12. A process-of numufucture of rolled steel members according to claim 8, wherein 'the steel of which the member is composed is chrome-steel containing a small proportion of a cluingre-point di'xpressant.

In testimony whereof wc-hare signed our nai'nes to this specification.

NARAINA D A S CH( )PRA. FREDERICK J )HN l5 ULLEN. 

